Dual laser-beam synchronous self-fusion welding of Ti–6Al–4V titanium alloys T-joints based on prefabricated welding materials

Abstract

Aiming at the difficulty of feeding filler wire in the dual laser-beam synchronous welding (DLSW) of Ti–6Al–4V titanium alloys T-joints, the self-fusion DLSW process based on prefabricated welding materials on the stringer was developed. Prefabricated bosses on both sides of the stringer were used as welding materials. In this paper, the influence of boss size and laser power on the weld formation was studied. The influence of microstructure transformation on mechanical properties was demonstrated. It is found that T-joints with desirable weld formation can be obtained when the boss size of 0.8 × 0.8 mm2 was applied. The temperature distribution of the T-joint during laser welding process was obtained by finite element simulation method. It indicates that the cooling rate of fusion zone is 140 °C/s, indicating that massive transformation occurs in the fusion zone. The microstructure of fusion zone characterized by acicular martensite plates α′ and a small amount of intergranular α phase meets with the cooling rate of FZ. Due to multiple strengthening effects, the average microhardness of fusion zone is 351.6 HV, which is higher than the average microhardness of base material. The pull-out strength of T-joint is not related to the weld penetration, and its average pull-out strength is 1035.5 MPa. The fracture occurred in the weld toe of the pull-out specimen, and fracture surface presents quasi-cleavage fracture characteristics.